1. Field of the Invention
The present invention relates to a resist technology, and more particularly, to a pattern-forming resist material suitable for forming negative resist patterns using deep ultraviolet (UV) radiation as an exposure radiation. The resist patterns are usually formed on a substrate or base material, i.e., a semiconductor material, during the production of semiconductor devices such as large-scale integrated (LSI) circuits, very-large-scale integrated (VLSI) circuits, and bubble memory devices. The present invention also relates to a process for the formation of resist patterns using said resist material.
2. Description of the Related Art
To attain a desired fine fabrication in the production of LSIs, VLSIs and other semiconductor devices, a plurality of pattern-forming resist materials such as rubber-like resists, photocomposable polymeric resists and novolac resin resists, as well as different exposure radiations such as ultraviolet (UV) rays, electron beams, X-rays, and ion beams, are widely used. Recently, deep UV radiation has replaced the usual UV radiation, as the deep UV radiation has a wavelength of about 200 to 300 nm, which is shorter than that of the usual UV radiation, and can satisfy the requirements for a greater a degree of fine fabrication in the resulting resist patterns. Note, it is known that various intensive research projects and development of deep UV resists have been carried out by persons skilled in the art, and in this connection, as suitable deep UV resists, it has been proposed to use photodecomposable polymeric resins, or novolac resists, which are well known as the UV resists and can be used without modification. These deep UV resists, however, have several drawbacks; the photo decomposable polymeric resins have a poor sensitivity to deep UV and a resistance to dry etching such as oxygen plasma etching, and the novolac resists show an unsatisfactory pattern resolution due to an excessively high light absorption of the benzene ring included therein.
In addition to these resists, it has been proposed to use cross-linking resists wherein a cross-linkable polymer such as polyvinyl alcohol is combined with a cross-linking agent such as diazonium salts, but these resists have an unsatisfactory pattern resolution due to swelling of the resulting resist patterns. The reason for the swelling of the resist patterns is as follows: ##STR1## wherein n denotes a polymerization degree, and a diazonium salt of the formula: ##STR2## as a cross-linking agent is used as a resist material, and the resist material is selectively exposed to deep UV radiation, PVA in the exposed areas becomes insoluble in water as a result of a cross-linking reaction thereof. The water-insoluble resist pattern thus formed is represented by the following formula: ##STR3## in which n is as defined above. This cross-linking reaction, however, occurs at a small portion of hydroxyl groups in PVA, because the concentration of the cross-linker is low. And thus, since the most of hydroxyl groups in PVA remains unchanged, the polymer remains hydrophilic even after the cross-linking reaction. Therefore, during development, water diffuses into the polymer and results in swelling.